Each front wheel of a four-wheel vehicle is provided with a certain fixed toe angle with the aim of ensuring a driving stability of the vehicle, in addition to a steering angle which is varied as required for changing the traveling direction of the vehicle. In recent years, there have been proposals to equip a vehicle with a device for varying the toe angles of the rear wheels to the end of improving the driving stability and response.
Japanese patent publication No. 9-030438 discloses a device that includes a pair of electric linear actuators each provided at a junction between a lateral link or a trailing link of a corresponding side a vehicle suspension system and the vehicle body so that the toe angle of the rear wheels may be varied individually.
It was also proposed in Japanese patent publication No. 2008-04981 (by the inventor of the present application and two others, and corresponds to U.S. patent application Ser. No. 11/830,391 and EP patent No. 1892180B) to control the toe angles of the rear wheels to be symmetric to each other or otherwise come to agree with each other if the control of either one of the toe angles becomes faulty or incapacitated for any reason.
However, according to the previous proposal in the aforementioned Japanese patent publication, when a rear wheel of a faulty side is seized or get stuck at a certain angle, it may be possible to keep the vehicle travelling straight ahead but the tires of the rear wheels are subjected to uneven or excessive wears.